This invention relates to cages for confining animals, particularly to those for experimental animals of smaller size such as mice and rats. More specifically, the invention deals with a hermetically sealed, ventilated cage suitable for confining and rearing relatively small experimental animals in a germ free, hygienically favorable environment. The cage in accordance with the invention lends itself to advantageous use where a multiplicity (e.g. tens or even hundreds) of such cages are arranged in columns and rows.
The laboratory animal cage has been known and used extensively which comprises a molded plastic casing or enclosure in the form of an open top box, with a wirework lid closing the open top of the casisng for confining an experimental animal or animals. For feeding the confined animal, a water dispenser has been employed which has an elongate spout inserted in the casing through a hole formed in a side or end wall of the casing. U.S. Pat. No. 4,346,672 to Niki describes and claims an example of such water dispenser.
One of the problems heretofore encountered with this type of cage is the sealing of the joint between the spout of the water dispenser and the edge of the casing bounding the hole receiving the spout. Conventionally, the hole has been shaped and sized for a close fit with the dispenser spout. However, since the plastic casing is usually autoclaved preparatory to use, the hole has been susceptible to thermal deformation, making it difficult or impossible to closely insert the dispenser spout in the hole. Such difficulty has become even more pronounced in the case of large scale experiments involving the use of tens or hundreds of animals that must be kept in separate cages.
Another problem with the prior art cage also arises in connection with the water dispenser, which is so constructed as to dispense water as the caged animal prods at the tip of the dispenser spout. However, moving about within the cage, the animal may touch or sport with the spout, with the consequent leaking of water therefrom. Moreover, because of the construction of the prior art water dispenser, water has also been easy to spill from the spout even when the animal is drinking therefrom in the normal manner. Such water spillage is objectionable from the standpoint of animal hygiene because, collecting on the bottom of the casing, the water can chill the body of the animal and so reduce its weight. The loss of weight can seriously affect the experiment if, for example, drugs are being tested on the animal.
The supply of water from the spout can also be easily impeded by the wood chips usually laid on the bottom of the cage in rearing mice, rats or the like. The prior art cage construction has allowed the wood chips to pile up near the tip of the dispenser spout with the movement of the caged animal. Such a pile of wood chips can easily touch and activate the dispenser spout thereby causing water spillage therefrom. Further the water dispenser has been prone to malfunctioning, failing to discharge water, as the wood chips are caught in the tip of the spout. The possible result has been the death of the animal in the worst case, totally invalidating the experiment.
It has also been proposed to hermetically close the open top casing of the cage with a solid outer lid, which overlies a wirework inner lid, and to ventilate the interior of the casing with germ free air. The caged animals may be infected with germs. The air exhausted from within the cage may contain such germs. Should such air be allowed to fill the laborary, the experimenters might be infected with the germs or might develop an allergy. It is therefore important that the cage be sealed hermetically and be ventilated so as not to contaminate the laboratory air.
Thus the ventilation system requires not only a conduit for supplying germ free air into the cage but also another conduit for exhausting the possibly contaminated air from within the cage. Further, as these conduits are inserted in the cage through holes formed therein, the gaps between the conduits and the edges of the holes must be sealed against the escape of the contaminated cage air. As far as the applicant is aware, there has been suggested no truly satisfactory method of readily connecting the air supply and exhaust conduits, as well as the spout of the water dispenser, to the cage so as to prevent the outflow of the contaminated air therefrom.